The present invention relates to apparatus for dispensing particulate material and in particular to a developer apparatus for applying toner material to the surface of an imaging member in an electrostatographic reproducing apparatus.
In an electrostatographic reproducing apparatus commonly in use today, a photoconductive insulating member is typically charged to uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an an electrostatic latent image on the member which corresponds to the image areas contained within the usual document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material which comprises both charged carrier particles and charged toner particles which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas in the photoconductive insulating area to form a powder image on the photoconductive area. Alternatively, single component development systems may be employed which utilize only toner particles. The developed image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating or by the application of pressure.
In most commercial applications the particulate toner material is contained in a sump and dispensed therefrom by gravity feeding. Typically this requires a fairly extensive vertical dimension for the toner sump and developer dispenser which is unacceptable in the design of compact automatic printing apparatus. Furthermore, with the emergence of the cartridge concept wherein one or more functional units of the electrostatographic reproducing apparatus such as the imaging member, developer housing, cleaner housing, and charge corotron may be included within a removable processing cartridge which may be discarded upon exhaustion of supply of developer, life of photoreceptor or filling of the cleaner sump and replaced with a new processing cartridge there are several architectural constraints on the design and placement of a toner sump. In these configurations, it is frequently desired to have a generally horizontally oriented toner sump and developer housing rather than the previously mentioned vertically oriented toner sump and developer housing. In such a housing, it is therefore necessary to physically transport toner from the sump portion to the developer housing. This is particularly important in those types of developing systems wherein it is necessary to maintain a supply of toner in a nip between a toner donor roll and a charge metering roll to supply an adequate quantity of charged toner to the imaging member during development. Paddle wheels have previously been employed to move toner in such a manner. However, they generally have been found to be inefficient in that they generally do not have access to the entire volume of the sump portion of the developer housing. Accordingly, there is a desire to provide a simple, inexpensive way to transport toner horizontally and efficiently in a developer housing.